This invention relates to an electric typewriter or similar machine and more particularly to a clutch mechanism for use with a platen for such machines which will selectively permit the platen to be vertically indexed either automatically line-by-line or manually in a free-wheel, vernier fashion.
Electric typewriters or similar machines generally have a platen fixed to a central shaft supported for rotation in a frame member. The page which is being typed is pressed into frictional engagement with the platen and as the platen is rotated, the page is vertically advanced to present a fresh surface for typing. During normal typing, the platen is advanced line-by-line with a predetermined spacing between each line. This is generally done by actuating a pawl which is in engagement with a line indexing ratchet wheel which is in turn connected through a clutch to and is concentric with the platen. Each time it is desired to type a fresh line, the pawl is actuated to rotate the line indexing ratchet wheel predetermined distance, which then rotates the platen a predetermined distance. Thus, the page is advanced to present a fresh line.
The clutch between the line indexing wheel and the platen is provided so that the platen may be rotated independently of the ratchet wheel when the clutch is disengaged. Clutches for disengaging the platen from the line indexing ratchet wheel as known in the art comprise mating gears on the platen and a clutch member which is connected to the ratchet wheel. To disengage the platen and ratchet wheel, the clutch member is axially moved out of meshing engagement with the platen gear and relative to the line indexing ratchet wheel. To avoid play in the connection between the line indexing ratchet wheel and the clutch element, yet allow relative movement therebetween, has not been adequately solved in a simple manner by the prior art, one example of which is German Provisional Pat. No. 2,242,074 which accommodates play by adjusting the radial spacing of the clutch member gear teeth relative to the platen gear teeth.